Treatment of congenital heart disease typically requires surgical intervention, such as “open-heart” surgery during which the thoracic cavity is opened and the heart, arteries/veins and/or associated valves are repaired or otherwise treated. Postoperative complications that may appear during short and long-term patient follow-up include heart valve dysfunction. For example, tetrology of fallot is a congenital heart defect often discovered at birth, in which a baby appears blue as a result of an obstruction affecting the proper functioning of the pulmonary valve of the heart. The obstruction is often surgically removed at an early age to improve the chances that the baby will survive. The surgical procedure typically results in subsequent leaking (i.e., regurgitation) of blood through the pulmonary valve. Over the life of the patient, the regurgitation may become more severe and result in further dysfunction of the heart valve due to, for example, dilation of the heart chamber and heart valve, by the body, to compensate for the increased regurgitation.
Approximately 89,000-95,000 open-heart surgeries are performed each year to address and resolve heart valve dysfunction. The surgery requires an incision, under general anesthesia, that transects the sternum in half vertically from just below the larynx to above the diaphragm. The heart is stopped or arrested during the surgery by infusing cold saline with high potassium content. A heart-lung machine then drains the deoxygenated blood from a tube placed in the right atrium and pumps it through an oxygenator. The oxygenator has a blood gas membrane that allows carbon dioxide to leave the blood while oxygen is diffused into the blood. The oxygenated blood is then returned to the patient through a tube that runs into the aorta, above the valve. This surgery is very expensive and requires a prolonged recovery period in the hospital with additional rehabilitation once the patient is discharged. This invasive surgery also results in a large chest scar.
Heart valve dysfunction includes, for example, pulmonary regurgitation, which occurs when the heart valve in the main pulmonary artery between the heart and the lungs, is unable to prevent the backflow of blood to the right ventricle of the heart. The dysfunction of this heart valve leads to a volume load on the right ventricle and causes right ventricular dilation, which can lead to right ventricular dysfunction which is thought to contribute to ventricular tachycardia and sudden death.
Due to the long-term deleterious effects of severe pulmonary regurgitation, surgical pulmonary valve replacement is performed for patients with severe regurgitation, symptoms of exercise intolerance and/or progressive right ventricular dilation and dysfunction.
Cardiologists typically defer the valve replacement procedure as long as possible, because of: the need for a repeat open-heart surgery; the risks of surgery and cardiopulmonary bypass; and the limited lifespan of all available surgically-implanted valves. The risks associated with surgical valve replacement are particularly acute with respect to pediatric patients in that the replacement valves do not grow with the patient and thus require more frequent replacement.
Prosthetic heart valves used to replace diseased or abnormal natural heart valves are typically mechanical devices with, for example, a rigid orifice ring and rigid hinged leaflets or ball-and-cage assemblies. Prosthetic heart valves are, more recently, bioprosthetic devices that combine a mechanical assembly with biological material (e.g., human, porcine, bovine, or biopolymer leaflets). Many bioprosthetic valves include an additional support structure, such as a stent, to support the leaflets of the valve. The stent also absorbs the stresses, which would otherwise be borne by the leaflets, from the hemodynamic pressure exerted during normal heart operation.
Heart valve replacement, typically, involves the surgical implantation of the valve prosthesis during open heart surgery and requires the use of a heart and lung machine for external circulation of the blood as the heart is stopped and the artificial valve prosthesis is sewed in. Valve replacement surgery is thus very demanding on the patient's body and may, therefore, not be a viable technique for patients that are physically weak due to age or illness. Accordingly, it is desirable to develop a heart valve replacement apparatus and procedure that is minimally invasive and does not have the morbidity of a re-operation.